To reduce costs associated with the manufacture of positive displacement pumps, especially those of the type used in food applications, it is desirable to utilize materials less expensive than conventional brass and stainless steel materials used to make the pump housing. Plastic materials suitable for use as a pump housing material for food applications typically must be suitable for use in high temperature conditions, which conditions often exceed 300 degrees F. The use of plastics is also advantageous to eliminate sources of lead from the pump system. In food and drinking water applications, this is a very desirable feature.
Glass filled plastics are often suitable for use in such high temperatures, however, guidelines typically associated with the use of plastics in food applications, such as those set forth by NSF International, typically limit the amount of glass fiber exposed to the surface of wetted parts, such as interior surfaces of the pump housing, to one inch of exposed glass fiber or less. As a practical matter, if significant secondary machining of the plastic part is required, the level of exposed fiber will usually exceed the limit.
Conventional molds and molding techniques desire improvement in connection with the manufacture of plastic pump housings. Such molds and techniques result in housings requiring significant secondary machining, and thus are unsuited for making housings for food applications.
Accordingly, what is desired is an improved method of making a plastic housing that is suitable for food applications and, as molded is ready for use and any additional machining needed is de minimis and less than about one square inch of the wetted interior surface is subjected to further machining after being formed by molding.